Many different types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. Examples of digital printing systems in current use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; thermal wax printers; dye diffusion thermal transfer printers; and ink jet printers. However, at present, such electronic printing systems have not significantly replaced mechanical printing presses, even though this conventional method requires very expensive setup and is seldom commercially viable unless a few thousand copies of a particular page are to be printed. Thus, there is a need for improved digitally controlled printing systems, for example, being able to produce high-quality color images at a high speed and low cost, using standard paper.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of, e.g., its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop-on-demand ink jet. Continuous ink jet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell.
Conventional continuous ink jet printing utilizes electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a "catcher") may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium. U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.K. Patent Application GB 2 041 831A discloses a mechanism in which a deflector steers an ink jet by the Coanda (wall attachment) effect. The degree of deflection can be varied by moving the position of the deflector or by changing the amplitude of perturbations in the jet.
In commonly assigned, co-pending U.S. patent application Ser. No. 08/954,317, now U.S. Pat. No. 6,079,821, entitled CONTINUOUS INK JET PRINTER WITH ASYMMETRIC HEATING DROP DEFLECTION, filed in the names of Chwalek, Jeanmaire, and Anagnostopoulos on Oct. 17, 1997, an ink jet printer includes a delivery channel for pressurized ink to establish a continuous flow of ink in a stream flowing from a nozzle bore. A heater having a selectively-actuated section associated with only a portion of the nozzle bore perimeter causes the stream to break up into a plurality of droplets at a position spaced from the heater. Actuation of the heater section produces an asymmetric application of heat to the stream to control the direction of the stream between a print direction and a non-print direction.
It was also disclosed in the above-cited co-pending application that, using semiconductor VLSI fabrication processes and equipment, and by incorporating addressing and driving circuits on the same silicon substrate as the nozzles, a dense linear array of nozzles can be produced. Such arrays can be many inches long and contain thousands of nozzles, thus eliminating the need to scan the print head across the page. In addition, inkjet printers may contain multiple arrays, all of which may be located on the same silicon substrate. Each array could then emit a different color ink. Full-width and full-color ink jet printers can thus be manufactured, which can print at high speeds and produce high-quality color prints.